Landfill
A Landfill Site is the ultimate destination for waste, ideally after all forms of Reuse, Recycling, and Recovery have been undertaken and as such it is at the bottom of the Waste Hierarchy.
Introduction
The Definition of 'Landfill' is found in the Landfill Directive 1999/31/EC on the landfilling of waste as 'a waste disposal site for the deposit of waste onto or into land (i.e.underground) including:
- internal waste disposal sites (i.e. landfill where a producer of waste is carrying out its own waste disposal at a place of production), and
- a permanent site (i.e. more than one year) which is used for temporary storage of waste'.
The deposit of waste into a Landfill site has evolved in the UK from 'open tips' and uncontrolled tipping in the late 1960's through to the current position comprising highly engineered solutions that contain and stabilize the waste in a 'Sanitary Landfill' - the complexity of the engineering approach and management being based upon the nature of the waste received and the sensitivity of the location of the site, especially in the context of the quality of the underlying groundwater.
Landfill sites have usually been constructed in disused quarries, or parts of quarries. However, the phrase is also used to describe sites built where there had previously been no excavation. Such sites are also known as “land-raise” sites, but in the context of this website, no distinction has been made. To all practical intents and purposes, there is no significant difference between landfill and land-raise.
Whilst Landfill is the ultimate destination for waste, ideally after all forms of Reuse, Recycling, and Recovery have been undertaken, there there will always be a small element of waste that will need to be landfilled in a safe and secure way (under the Landfill Directive no more than 10% of MSW generated by weight is to be landfilled by 2035). In developing countries, with limited infrastructure, the delivery of Sanitary Landfill would represent a huge step forwards in protecting water resources and human health.
The key legal requirements for managing landfill have been implemented in the UK through the Landfill Regulations 2005 which implemented the Landfill Directive and defined 3 types of Landfill:
and the standards are set out for the key stages of landfill in regards to:
- location
- engineering
- management
- closure and
- monitoring for landfills
Landfill Overview
The placement of waste in a landfill will slowly degrade over time, and in the case of the presence of Organic Waste within the Residual Waste going to landfill, it will breakdown to produce Landfill Gas and Leachate which have the potential to cause environmental pollution.
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| Landfill Cross-Section of Older, Dilute and Disperse Style Landfill, no Engineering Containment | Cross-Section of Modern Engineered Landfill |
The 'go-to' guidance for many in the landfill sector in the UK is still the waste management papers produced in the mid and late 1990's:
- Waste Management Paper 26B (WMP26B): Landfill Design, Construction and Operational Practice
- Waste Management Paper 26A (WMP26A): Landfill Completion
- Waste Management Paper 27 (WMP27): Landfill Gas
Groundwater and Hydrogeology
One definition of aquifer is as follows, quoted from Freeze and Cherry (1979): “An aquifer is best described as a saturated permeable geologic unit that can transmit significant quantities of waste under ordinary hydraulic gradients”. This definition captures the essence of the word very well.
In the England and Wales, the EA categorize aquifers to be consistent with the Water Framework Directive. The categories are Principal Aquifer, Secondary Aquifer and Unproductive Strata. Previously the phrases major aquifer and minor aquifer were utilized. Similar arrangements exist in Scotland and are supervised by SEPA.
The relevance of the hydrogeological setting within which a landfill is located arises from the need to assess the technical precautions required for a landfill to be authorized such that unacceptable environmental impacts are prevented. This assessment is undertaken via a Hydrogeological Risk Assessment (HRA); this is submitted as supporting document to an Environmental Permit application. Again, similar arrangements are in place in Scotland.
Leachate
Putrescible waste placed in landfill sites undergoes decomposition. This is also described in WMP26B. The process gives rise to a liquid known as leachate. Leachate arises from water entering the waste matter, generally from rainfall on open areas of waste. Leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Landfill leachate is strongly polluting in the external environment; one of the principal reasons for constructing landfill sites as containment facilities is to prevent landfill leachate from escaping from the waste mass in an uncontrolled manner.
Once the design of sites moved from dilute and disperse to containment designs, it became necessary to devise means of avoiding leachate from building up excessively within the waste mass. There are two drivers for this: (i) in extreme circumstances, the volumes could lead to levels over-topping the sides of any containment structures and leaving the site, and (ii) designing the site to maintain levels at a level as low as practically possible would improve the HRA outcome for any given design. Consequently, sites were designed with means to collect and remove leachate.
Leachate removed from the waste mass needs to be disposed of in an appropriate fashion. In general, this requires transmission to an appropriate treatment plant; this might be via a sewered connection to a sewage treatment plant operated by a utility company, or an on-site private leachate treatment plant. Depending upon the capacity at the receiving utility treatment plant, leachate may require pre-treatment at the landfill site.
A leachate treatment plant may discharge to a receiving watercourse or (less frequently) soakaway. Such a discharge would be regulated by the EA with an Environmental Permit. Discharge to a sewer, with or without pre-treatment, would require agreement with the relevant utility company.
Leachate may also be taken to an off-site facility (e.g utility sewage treatment works) via road-going tanker for disposal.
Landfill Engineering
Landfill engineering is a phrase used to describe the preparation and on-going engineering required to operate a landfill site.
What is required at any particular site depends upon the proposals made by the permit holder in order to be granted an Environmental Permit and any subsequent modifications agreed between the permit holder and the regulator (EA, NRW or SEPA).
The technical precautions required to operate a landfill are incorporated into the landfill engineering design. Notwithstanding that, there are minimum requirements imposed by the Landfill Directive and subsequent UK legislation – The Landfill (England and Wales) Regulations 2002 and the Landfill Regulations 2005.
The design will have been produced taking heed of the technical precautions required to satisfy the regulator that the site will not have an unacceptable impact upon the environment and that the approved design will comply with the requirements of the Landfill Directive. These precautions will have been validated against the various risk assessments required to accompany a permit application.
Usually the application will be accompanied by risk assessments of the hydrogeological impact of the site, the potential for landfill gas release and the stability of any engineering designs proposed. There will be additional risk assessments required for operational matters such as dust, noise and amenity impacts; these are largely managed by operational techniques, but occasionally there will be elements of mitigation required that constitute site engineering (e.g. the construction of noise bunds).
Sites which were authorised historically did not require engineering and such sites without an engineered lining system are commonly described as “dilute and disperse”. Notwithstanding the lack of site engineering, some evaluation of their pollution potential was undertaken. This mainly consisted of a simple evaluation of the ability of the surrounding geology to adsorb contamination to determine likely consequential pollution effects. This evaluation considered the ability of the ground to “dilute and disperse” the impact of the site, hence the common name.
Landfill engineering design evolved in the 1980s, such that new dilute and disperse sites became less likely to be granted consent to operate. At the time, this was not supported by the implementation of any new specific legislative drivers, the principal legislation remaining the Control of Pollution Act 1974. This required landfills to be licensed by local authorities. In assessing licence applications, local authorities were required to ensure the prevention of pollution to water and danger to public health. This requirement established a rationale for assessment and its implementation evolved over the period from 1976 onwards.
Landfill sites that incorporate engineered barriers are known as “containment facilities”. The design of such facilities has more than one form and can incorporate different numbers of layers and different designs. These layers are conventionally known as the “landfill lining system”.
The Department of the Environment produced a series of Waste Management Papers (WMP) over the period from the late 1970s to 1997. WMP 26B contains a review of the types of designs. The design employed at any particular design would be informed by the outcome of the HRA which would assess the likely impact of a site upon the environment taking account of the design proposed. In general terms, the most sensitive sites would require the greatest degree of engineering.
Landfills are constructed in discrete parts known as “landfill cells”. The sub-division into cells is undertaken so as to minimise the operating area and consequently minimise leachate generation and make the site more manageable in terms of odour and litter control. Sub-division also enables the site engineering to be constructed progressively as the site fills.
Landfill Gas
Another product of waste decomposition is landfill gas. This is a mixture of various components, principally methane. WMP26B also contains a useful review of the generation and evolution of landfill gas.
Landfill gas needs to be managed to prevent build-up, migration in the surrounding soils and rock and release to the atmosphere.
Management of landfill gas consists of prevention of migration and escape by containment barrier, active removal of the gas from the waste mass by extraction and subsequent destruction.
Landfill gas can be utilized for energy generation – principally electricity generation – as well as simple destruction by combustion in a flare.
WMP27 deals with methods for management of landfill gas.
Electricity generated from landfill gas can be used on-site and also be supplied to the National Grid for re-sale.
Landfills in the UK
Set out the criteria for location - geology, hydrogeology, historical context
Set out the sites in the UK and the location map of sites in the UK here?
Landfill Management
Landfill Restoration and Closure
Landfill sites are generally restored (finished) to green space, such as agriculture, forestry or (less often) public open space.
The final engineering structure constructed is a capping layer on top of the final layer of waste. Sub-soil and then top soil is placed on to the engineered capping layer. Landfill sites are usually restored progressively in phases as the waste mass reached final levels. The final restoration is usually defined in the Planning Permission for the site.
The engineered cap can be constructed in several ways and the design selected is evaluated in the same way as the landfill lining system, taking account of the various engineering constraints and impacts to be avoided at each site. The design also undergoes similar risk assessment to the lining system.
The final layer of waste is usually covered with a thick layer of cover, known as the final cover (see diagram above).
Commonly, the capping layer will consist of a compacted clay layer of 1 metre thickness. This can be replaced or supplemented by flexible membranes such as LLDPE (Linear Low Density Polyethylene) or GCL (Geo-synthetic Clay) in varying combinations. Membranes can be laid in an over-lapped but unjoined fashion or can be overlapped and welded similar to lining systems.
Soil thickness will depend upon the proposed afteruse of the site; uses involving deep-rooted plants will require thicker soils to protect the engineered capping layer from root-penetration.
Gas and leachate extraction and monitoring equipment (such as monitoring well and pipework) commonly penetrates the capping and soil layers in order to afford access for maintenance and monitoring. Sometimes this equipment is progressivly buried with suitable access points remaining at the surface; this is done principally for aesthetic reasons to improve the appearance of the final restored surface.
Landfill sites where all tipping has ceased and the all infrastructure for post-closure management has been installed are deemed "closed" following agreement with the EA.
The landfill operator is required to continue to maintain monitoring and management of the site post-closure until it can be shown to the satisfaction of the EA that the active management of the site by the operator is no longer required. Assessment of such a state is measured against criteria identified in WMP 26A and subsequent EA guidance. It is generally accepted for non-hazardous landfill sites that this is unlikely to be able to shown for at least 60 years post-closure, probably somewhat longer.
Settlement and Surcharge
As the waste mass decomposes, the fill material settles under its own weight to occupy less volume. This process is known as settlement.
Settlement in landfilled waste occurs due to loading and other processes including chemical and microbial actions. These processes are time-dependent, and are controlled by factors such as leachate composition, pH, temperature and moisture. As a result, settlement in landfilled waste, especially long-term settlement, is complex and difficult to predict in both magnitude and timing. Notwithstanding that, reasonably accurate estimates are commonly used.
Landfill sites operate under the terms of a Planning Permission. Amongst the matters controlled by the permission will be the final levels to which the site must be restored. As the waste ages and decomposes the final level will settle to a lower level. In order to ensure that the agreed final levels are achieved after the majority of the decomposition and related settlement have finished, it is common to agree that the final levels can be exceeded initially - known as surcharging.
The degree of surcharging permitted is agreed as a Landfill Surcharge Allowance. This figure is usually quoted as a percentage which relates to the depth of the site at each point. The percentage agreed between the planning authority and the developer will vary according to the nature of the waste accepted, the depth of fill and the morphology of the landfill void.
It is conventional to have two sets of contours agreed with the planning authority - pre-settlement and post-settlement. The latter represent the level to which the site can be surcharged, the latter represent the levels to which the site will settle. The post-settlement contours are sometimes also known as final levels.
Landfill Settlement Contours are the levels to which a surcharged landfill can filled.
Landfill Monitoring
Landfill sites are monitored to ensure that all activities are being undertaken in compliance with permit and other regulatory requirements. Furthermore, monitoring is undertaken to ensure that any impacts derived from the site are not unacceptable nor cause nuisance.
Various aspects of the landfill are monitored, such as:
- Quantity and type of waste received including any assessments of suitablity for acceptance at the site
- Daily activity and waste placement log
- Leachate volume and quality within the waste mass
- Leachate volume and quality extracted from the site and disposed
- Landfill gas quantity and quality within the waste mass
- Presence of landfill gas outside the site perimeter
- Emissions of landfill gas from the surface of the site
- Groundwater quality outside the perimeter of the site
- Surface water quality in nearby water bodies
- Noise emissions associated with the site
- Dust emissions associated with the site
- Odour emissions associated with the site
- Pest activity (e.g. birds, rodents) in, on and around the site
- Complaint records held at the site
Leachate, groundwater and surface water monitoring
The specific reasons for leachate, groundwater and surface water monitoring at landfills are:
- to demonstrate that the landfill is performing as designed;
- to provide reassurance that leachate controls are preventing pollution of the environment (by reference to a pre-established baseline);
- to meet the control and monitoring requirements of legislation and in particular Regulations 14 and 15, as well as Schedule III, of the Landfill Regulations, this includes the requirement for control monitoring;
- to demonstrate compliance with the Groundwater Control and Trigger level requirements of Schedule 3 of the Landfill Regulations;
- to indicate whether further investigation is required and, where the risks are unacceptable, the need for measures to prevent, reduce or remove pollution by leachate;
- to identify when a site no longer presents a significant risk of pollution or harm to human health (to enable an application for a certificate of completion to be made, and thereby formally end the licensing or permitting process and the legal duty to monitor).
There is considerable published guidance available on how, when and why to undertake this monitoring.